We definitely have an overpopulation problem, but the solutions are not going to be pretty.
The world will get a lot more violent, or disease and starvation will even it out. It's tough to say.
If I didn't have kids I'd be a lot less worried about it. I say, "well, hopefully humans will either slow down their reproduction rate or find some amazing technologies for sustaining 7-10 billion people (it should reach 10 billion by about the year 2060).
We Americans are actually in pretty good shape. I've researched this a lot, and what I learned about agriculture is interesting.
For example:
1. A person who eats a vegetarian diet needs about .75 acres of farmland to be sustained. If we round that, then we say that you need about one acre per person per year.
2. The United States has about 7 acres of farm-able land per human being in our nation. So we're safe, right?
3. Not so quick. A. Most of us are omnivores. Secondly, we eat a lot of processed and packaged foods. Thirdly, we eat too much (I know I'm as guilty as the next guy--I need to lose about 20-25lbs).
4. When the dust settles and the math is in, it's a simple fact that Americans, on average, eat 10 acres per year. That's pretty bad.
You might be thinking, "wait a minute. How is it possible for Americans to eat, on average, 10 acres per year when there's only 7 acres per person?
Imports.
Just like oil, Americans are importing more and more food each year. Right now most of our food is produced domestically (like oil was back in the 40s, 50s, and 60s). But like oil, we want more and more food, so we import.
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Now, let's look at China. The Chinese actually have about .75 acres per person. They hit their limit. Of course, some people eat more than others, and some eat meat (which uses a LOT of land). That's why in China people have traditionally (in some areas) struggled with famine. There simply isn't enough land to grow the crops needed to feed all those people. BTW: They import food too.
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Let's look at the opposite: New Zealand. They are in a unique position as they have 20 acres of farmable land for each citizen. That's amazing. New Zealand is roughly the size of California, but with about 10% of California's population. New Zealand has a lot of good farmland. So they are in great shape and won't starve anytime soon.
Unfortunately for them, they don't have much oil, so they grow a ton of sheep on their land and use that resource to trade for oil. They'll have to figure out something someday in terms of energy, because oil will become more and more expensive. How many sheep or how much wool is needed to gain a barrel of oil?
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The solution to the planet's problem is one that will most likely never be done: sterilization.
It's humane, but goes against the beliefs of many. I don't even know how I feel about it. I'm Christian, and follow the teachings of the Bible, but am often unclear on whether sterilization is right or wrong.
But if done by lottery, on a world-wide level, it would definitely work. If some children were randomly sterilized before hitting reproductive age it would certainly solve the problem of overpopulation, which would solve the symptoms as well (pollution, starvation, disease, etc.).
But it'll never happen.
Unfortunately, nature will work it out, and we might not like the results.